Characterization of Silicon Wafers with Combined Photocarrier Radiometry and Free Carrier Absorption

Abstract

A combined photocarrier radiometry (PCR) and free carrier absorption (FCA) technique was employed to evaluate the electronic transport properties (carrier lifetime $\tau$, diffusion coefficient $D$, and the front surface recombination velocity $S_{1})$ of silicon wafers and to monitor the ion implantation and thermal annealing processes in the semiconductor manufacturing. For non-implanted silicon wafers, the experimental results showed that the accuracy of the simultaneous determination of the transport properties was greatly improved by fitting simultaneously the measured PCR and FCA signals to the theoretical models via a multi-parameter fitting procedure. For As$^+$ ion implanted and thermal annealed silicon wafers, the results showed that both PCR and FCA amplitudes increased monotonically with the increasing implantation dose ($5\times 10^{11}$ cm$^{-2 }$ to $1\times 10^{16 }$ cm$^{-2})$, the decreasing implantation energy (20 keV to 140 keV), and the increasing annealing temperature (500 $^{\circ }$C to 1000 $^{\circ }$C), respectively. To explain the dependences of the PCR signals on the implantation and annealing parameters, a multi-wavelength PCR technique was proposed to extract the electronic transport properties of the implanted and annealed wafers. The results showed that ion implantation and thermal annealing caused significant decreases of the minority carrier lifetime and diffusion coefficient of the implantation layer, as well as the recombination velocity at the front surface. All three parameters decreased with the increasing implantation dose.